1. Field of Invention
The invention concerns an apparatus (FIG. 1) and a method (FIG. 2) for removal of ammonia from a medium.
The apparatus is designed so that the apparatus in one single container has a combined function for:                1. chemical process unit        2. separation of the liquid and the solid fractions        3. mixing of the medium        4. concentration of solids        5. heating        6. ammonium extraction        
The apparatus consist of a process container (including a heater system) in which an elevator unit is placed with a combined function for lift-sink, filtration, mixing and cleaning. The elevator unit is kept water tight to the process container by means of a flexible membrane, so that a positive pressure can be maintained inside the process container for improving the filtration. The function of the process container is to carry out the chemical processes; the elevator unit has to function as a flexible filtration unit and as a concentration facility in the regeneration step; the mixing-cleaning unit of the elevator unit has the dual function to mix the medium and to clean the filter and the container surface for precipitations. The result of this design is that all unit processes can be carried out in the same container, without transportation of MAP/medium between different containers, and without MAP being in contact with pumps and pipes. Only the medium without MAP is in contact with pipes, pumps and other containers before and after the chemical processes and the filtration have taken place.
The apparatus use a method for removal of ammonia from a polluted medium, where the medium in a first chemical process in the process container is supplied with minimum one reagent, which causes a chemical reaction between the ammonia of the medium and the added reagents containing magnesium and phosphorous and/or a magnesium phosphate salt (MP), which causes precipitation of minimum one first ammonium-containing salt (MAP) in the process container, where a simultaneous pressure-accelerated filtration also occur resulting in a separation of the purified medium and MAP, where MP/MAP are retained by the filter, where the purified medium are pressed through the filter. Following in time the first chemical process and in the same container, a sinking of the elevator unit and a heating of the tank cause that MAP salt concentrates and the thermal process causes that ammonia (A) are liberated from MAP and are evaporated from the medium, so that the first reagents in the first chemical process can be recovered as magnesium phosphate (MP) and reused, and ammonia gas can be collected as a concentrated gas. The apparatus are designed so that both the first chemical process (A+M+P-->MAP), separation of MAP/purified medium, mixing of medium and the regeneration of MP (MAP-->A+MP) are carried out in the same container.
2. Description of the Prior Art
It is already known from chemical reaction plants to add reagents to a medium with a following separation of precipitation products from the medium. It is also known that magnesium, phosphate and ammonia under specific process conditions precipitate as MAP. This process occurs for example in heat exchangers on biogas plants. Biological removals of ammonia by nitrification-denitrification, where ammonia are released as free nitrogen to the atmosphere are also a well known process. That ammonia can be regenerated from MAP by a thermal process is also known from laboratory tests.
Own tests of the described chemical processes in full scale, has shown that MAP and MP are reagents having very special physical/chemical properties. These properties complicate transportation in pipes due to clogging, and also complicate the use of pumps due to precipitations in the pumps. Furthermore the chemicals are very wearing on mechanical items. Own tests has shown that it is very difficult to control a separation of MAP and MP from a liquid by using traditional separation systems as cyclones, band filters and other “passive” filter systems. The complications are caused by the precipitation of MAP/MP on mechanical parts and the small diameter of MAP/MP. The best results have been achieved by using a fine-mashed filter operating under positive pressure.
Own tests has shown that the technical, operational and economic performance are Improved if a special produced pH regulated magnesium phosphate salt (MP-pH) are added to the first chemical process instead of adding M and P as single chemical where uncontrolled addition results in loss of chemicals, primarily phosphorous. The MP-pH is a solid, that is only soluble in a ammonia solution, and own tests has shown an improved reaction ability of the chemical after the thermal process and after short time in a water solution.